Managing over-current condition in a switching converter

Abstract

A switching converter provides an output voltage, and includes a first switch, a gate driver and an over-current management block. The gate driver is operable to drive the first switch with an ON duration of a first magnitude normally to provide the output voltage. The ON duration corresponds to a first phase of each cycle of a sequence of cycles of a periodic clock signal employed in the switching converter. The over-current management block is operable to determine a potential over-current condition when the switch operates with an ON duration of a first magnitude. In response to the determination, the over-current management block is operable to cause the gate driver to increase an ON duration of the first switch to a second magnitude, and examine a magnitude of current through the first switch with ON duration of the second magnitude to determine whether actual over-current condition is present.

What is claimed is: 
     
       1. A switching converter comprising:
 a first switch; 
 a gate driver operable to drive said first switch with an ON duration of a first magnitude normally to provide a first output voltage, wherein said ON duration corresponds to a first phase of each cycle of a sequence of cycles of a periodic clock signal; and 
 an over-current management block operable to: 
 check whether a potential over-current condition is present when said first switch operates with an ON duration of a first magnitude; 
 in response to a presence of potential over-current condition, cause said gate driver to increase an ON duration of said first switch to a second magnitude; and 
 examine a magnitude of current through the first switch with the ON duration of the second magnitude to determine whether an actual over-current condition is present. 
 
     
     
       2. The switching converter of  claim 1 , wherein said over-current management block is further operable to revert said ON duration to said first magnitude upon completion of said examination if said actual over-current condition is determined not to be present. 
     
     
       3. The switching converter of  claim 2 , wherein said examination, including said determination, is performed in a single cycle of said periodic clock signal with said ON duration equal to said second magnitude. 
     
     
       4. The switching converter of  claim 2 , wherein said over-current management block is further operable to cause said gate driver to switch off said first switch if said actual over-current condition is determined to be present. 
     
     
       5. The switching converter of  claim 2 , wherein said first switch is a high-side switch, wherein said switching converter further comprises a low-side switch in series with said high-side switch at a node,
 wherein a load current of said switching converter is drawn from said node, 
 wherein said actual over-current condition corresponds to a condition when said load current exceeds a safe limit, 
 wherein said gate driver drives said low-side switch to be ON in a second phase of each cycle of said sequence of cycles. 
 
     
     
       6. The switching converter of  claim 5 , wherein said gate driver receives said periodic clock signal and drives said high-side switch and said low-side switch to an ON condition normally according to the first phase and the second phase of said periodic clock signal respectively, but drives said high-side switch with duration of said first phase equaling said second magnitude upon determination by said over-current management block of said potential over-current condition. 
     
     
       7. The switching converter of  claim 6 , wherein said over-current management block concludes that a potential over-current condition exists if a current flowing through said low-side switch exceeds a first current threshold,
 wherein said first magnitude of duration for said first phase is insufficient to reliably determine presence of said actual overcurrent condition, 
 wherein said second magnitude of duration for said first phase is sufficient to reliably determine presence of said actual overcurrent condition, 
 wherein duration of said second phase is more than said second magnitude of duration. 
 
     
     
       8. The switching converter of  claim 7 , wherein said over-current management block concludes that a potential over-current condition exists if said current flowing through said low-side switch exceeds said first current threshold, or if an OFF-duration of said high-side switch is less than a second threshold duration. 
     
     
       9. The switching converter of  claim 8 , wherein said over-current management block comprises:
 a first current source to source into a first node, a scaled version of an inductor-current of said switching converter flowing through said low-side switch in second phases of each of said sequence of cycles; 
 a first current sink coupled in series with said first current source at said first node, said first current sink to sink from said first node, a scaled version of a maximum load current permitted to be drawn from said switching converter; and 
 a first inverter coupled to receive a difference current from said first node as an input, said first inverter to generate, as an output, a binary level indicating if said difference current is positive or negative to indicate said potential over-current condition. 
 
     
     
       10. The switching converter of  claim 9 , wherein said over-current management block further comprises:
 a timer coupled to receive as an input, said periodic clock signal, said period clock signal representing a pulse-width modulated (PWM) signal for operation of said high-side switch and said low-side switch, said timer to generate as an output a count value representing an OFF-duration of said PWM signal; and 
 a count comparator to compare said count value with a threshold count value representing a lower threshold for said OFF-durations to generate an output signal indicating whether an OFF-duration of said PWM signal is lesser than said lower threshold. 
 
     
     
       11. A switching converter comprising:
 a high-side switch coupled in series with a low-side switch at a node, wherein said high-side switch and said low-side switch are driven in an ON state or an OFF state according to a first internal clock and a second internal clock; 
 a gate driver operable to provide said first internal clock and said second internal clock based on an external clock having a sequence of cycles, with each cycle having a high level and a low level, duration of said high level being a first magnitude, 
 wherein said first internal clock, in a normal operation, is at said high level in durations said external clock is at said high level and at said low level in durations said external clock is at said low level such that said high-side switch is in said ON state with duration equaling said first magnitude in said normal operation, 
 wherein said second internal clock, in said normal operation, is at said low level in durations said external clock is at said high level and at said high level in durations said external clock is at said low level; and 
 an over-current management block operable to: 
 check whether a potential over-current condition is present during said normal operation; 
 in response to a presence of said potential over-current condition, cause said gate driver to increase duration of said high level of said first internal clock to a second magnitude such that said high-side switch is driven in said ON state for duration of said second magnitude; and 
 examine a magnitude of current through the high-side switch with the ON duration of said second magnitude to determine whether an actual over-current condition is present. 
 
     
     
       12. The switching converter of  claim 11 , wherein said over-current management block concludes that said potential over-current condition exists if current flowing through said low-side switch exceeds a first current threshold when said low-side switch is ON, or if an ON-duration of said low-side switch is less than a second threshold duration. 
     
     
       13. The switching converter of  claim 12 , wherein said over-current management block comprises:
 a first current source to source into a first node, a scaled version of an inductor-current of said switching converter flowing through said low-side switch in ON states of said low-side switch; 
 a first current sink coupled in series with said first current source at said first node, said first current sink to sink from said first node, a scaled version of a maximum load-current permitted to be drawn from said switching converter; and 
 a first inverter coupled to receive a difference current from said first node as an input, said first inverter to generate, as an output, a binary level indicating if said difference current is positive or negative to indicate said potential over-current condition. 
 
     
     
       14. The switching converter of  claim 13 , wherein said over-current management block further comprises:
 a timer coupled to receive as an input, said external clock, said external clock signal representing a pulse-width modulated (PWM) signal for operation of said high-side switch and said low-side switch, said timer to generate as an output a count value representing an OFF-duration of said PWM signal; and 
 a count comparator to compare said count value with a threshold count value representing a lower threshold for said OFF-durations to generate an output signal indicating whether an OFF-duration of said PWM signal is less than said lower threshold. 
 
     
     
       15. A voltage regulator module (VRM) comprising:
 a phase controller to generate a regulated supply voltage on a first supply node; 
 a first inductor coupled to the first supply node; and 
 a first smart power stage (SPS) comprising: 
 a first switch;
 a gate driver operable to drive said first switch with an ON duration of a first magnitude normally to provide said regulated supply voltage, wherein said ON duration corresponds to a first phase of each cycle of a sequence of cycles of a periodic clock signal; and 
 an over-current management block operable to: 
 check whether a potential over-current condition is present when said first switch operates with an ON duration of a first magnitude; 
 in response to a presence of potential over-current condition, cause said gate driver to increase an ON duration of said first switch to a second magnitude; and 
 examine a magnitude of current through the first switch with the ON duration of the second magnitude to determine whether an actual over-current condition is present. 
 
 
     
     
       16. The VRM of  claim 15 , wherein said over-current management block is further operable to revert said ON duration to said first magnitude upon completion of said examination if said actual over-current condition is determined not to be present. 
     
     
       17. The VRM of  claim 16 , wherein said examination, including said determination, is performed in a single cycle of said periodic clock signal with said ON duration equal to said second magnitude. 
     
     
       18. The VRM converter of  claim 16 , wherein said over-current management block is further operable to cause said gate driver to switch off said first switch if said actual over-current condition is determined to be present,
 wherein said first switch is a high-side switch, wherein said first SPS further comprises a low-side switch in series with said high-side switch at a node,
 wherein a load current of said first SPS is drawn from said node, 
 wherein said actual over-current condition corresponds to a condition when said load current exceeds a safe limit, and 
 wherein said gate driver drives said low-side switch to be ON in a second phase of each cycle of said sequence of cycles. 
 
 
     
     
       19. The VRM of  claim 18 , wherein said gate driver receives said periodic clock signal and drives said high-side switch and said low-side switch to an ON condition normally according to the first phase and the second phase of said periodic clock signal respectively, but drives said high-side switch with duration of said first phase equaling said second magnitude upon determination by said over-current management block of said potential over-current condition. 
     
     
       20. The VRM of  claim 19 , wherein said over-current management block concludes that the potential over-current condition exists if a current flowing through said low-side switch exceeds a first current threshold, or if an OFF-duration of said high-side switch is less than a second threshold duration,
 wherein said first magnitude of duration for said first phase is insufficient to reliably determine presence of said actual overcurrent condition, 
 wherein said second magnitude of duration for said first phase is sufficient to reliably determine presence of said actual overcurrent condition, 
 wherein duration of said second phase is more than said second magnitude of duration.